fade.c

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/// @file
/// Screen fades through the blend registers.
/// Part of runtime.c, the runtime object, compiled only through it.
 
#include "../runtime_internal.h"
 
enum {
  /// The layers the screen fades take: all but BG0.
  FADE_GAME_LAYERS = BLDCNT_TGT1_ALL & ~BLDCNT_TGT1_BG0,
  FADE_LAYER_MASK = BLDCNT_TGT1_ALL,
  FADE_BRIGHTEN = BLDCNT_EFFECT_LIGHTEN,
  FADE_DARKEN = BLDCNT_EFFECT_DARKEN,
  FADE_LEVEL_MAX = 16 ///< BLDY's strongest level: all white or all black.
};
 
/// Steps the screen fade once a frame, called by System_VBlankHandler: sets
/// BLDCNT to brighten or darken the chosen layers, moves BLDY one step from
/// the start level to the target level and counts gBlendFramesLeft down; at
/// the end it clears gBlendDuration.
void Fade_Update(void) {
  if (gBlendDuration != 0) {
    {
      volatile u16 *blendControl;
      u32 control;
 
      if (gBlendBrighten != 0) {
        control = gBlendLayers | FADE_BRIGHTEN;
        blendControl = &REG_BLDCNT;
      } else {
        control = gBlendLayers | FADE_DARKEN;
        blendControl = &REG_BLDCNT;
      }
      *blendControl = control;
    }
    {
      u8 *remaining = &gBlendFramesLeft;
      s32 delta;
      s32 level;
      s32 step;
 
      (*remaining)--;
      level = gBlendTargetLevel;
      delta = gBlendStartLevel - gBlendTargetLevel;
      step = *remaining;
      /* FAKEMATCH: an explicit libgcc call clobbers memory, so the zero test
       * reloads *remaining after it as the native does; with the / operator,
       * 37 instructions differ in every edition. */
      level += __divsi3(delta * step, gBlendDuration);
      REG_BLDY = level;
      if (*remaining == 0)
        gBlendDuration = 0;
    }
  }
}
 
// Screen fades. Fade_Update moves the fade one step each VBlank.
// The brightness (BLDY) runs from 0, the picture as drawn, to 16, all white
// or all black.
//   gBlendBrighten   : 0 fades toward black, 1 toward white
//   gBlendLayers     : the BLDCNT layers the fade covers
//   gBlendFramesLeft : frames until the fade ends
 
/// Fades BG1 to BG3, the sprites and the backdrop (0x3e) from the current
/// target brightness to `level` over `frames` frames.
#define FADE_DEFINE_BLEND(name, brighten, level)                               \
  void name(s32 frames) {                                                      \
    gBlendBrighten = brighten;                                                 \
    gBlendLayers = FADE_GAME_LAYERS;                                           \
    gBlendStartLevel = gBlendTargetLevel;                                      \
    gBlendTargetLevel = level;                                                 \
    gBlendDuration = frames;                                                   \
    gBlendFramesLeft = gBlendDuration;                                         \
  }
 
/// Fades out to black.
FADE_DEFINE_BLEND(Fade_ToBlack, 0, FADE_LEVEL_MAX)
 
/// Fades in from black.
FADE_DEFINE_BLEND(Fade_FromBlack, 0, 0)
 
/// Fades out to white.
FADE_DEFINE_BLEND(Fade_ToWhite, 1, FADE_LEVEL_MAX)
 
/// Fades in from white.
FADE_DEFINE_BLEND(Fade_FromWhite, 1, 0)
 
/// Starts a fade of any layers by setting the gBlend globals Fade_Update
/// steps. Reached through the far-call table.
///   bright : 0 toward black, 1 toward white
///   layer  : the BLDCNT layers to fade (low six bits)
///   start  : the starting brightness; above 16, the current target
///   target : the brightness to end at
///   frames : how long the fade takes
void Fade_Start(s8 bright, s32 layer, u32 start, s32 target, s32 frames) {
  gBlendBrighten = bright;
  gBlendLayers = layer & FADE_LAYER_MASK;
  if (start > FADE_LEVEL_MAX) {
    gBlendStartLevel = gBlendTargetLevel;
  } else {
    gBlendStartLevel = start;
  }
  gBlendTargetLevel = target;
  gBlendFramesLeft = (gBlendDuration = frames);
}
 
/// Waits a frame at a time until the running fade has finished. Called by the
/// title screen and the battle, and through the far-call table.
void Fade_Wait(void) {
  if (gBlendDuration != 0) {
    do {
      WaitFrames(1);
    } while (gBlendDuration != 0);
  }
}
 
#undef FADE_DEFINE_BLEND